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Cod liver oil capsules are dietary supplements rich in vitamin D, vitamin A and omega-3 fatty acids. They are a great source of supplemental nutrition, but can also cause some mild side effects, like bad breath and nausea.

Common cod liver oil side effects include bad breath, an upset stomach, headaches and a metallic taste in your mouth.
(Image: Photo by Cathy Scola/Moment/GettyImages)

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Common cod liver oil side effects include bad breath, an upset stomach, headaches and a metallic taste in your mouth. If you experience more severe side effects, like an allergic reaction, seek out medical attention immediately.

There is also the potential for more serious cod liver oil side effects like an allergic reaction or changes to your vision. Plus, cod liver oil pills may interact with medications you are taking. If you experience severe side effects, stop taking the supplement and seek medical attention right away.

Cod Liver Oil Pills

Cod liver oil pills are dietary supplements that provide vitamin A, vitamin D and omega-3 fatty acids. These nutrients occur naturally in food and play a variety of important roles in the body. However, since dietary supplements are not regulated by the U.S. Food & Drug Administration, it's not a given that the capsules contain what the ingredients list says, and health claims may not be true.

Vitamin A helps build and maintain healthy skin, teeth, mucus membranes, soft tissue and skeletal tissue. It also plays a role in eyesight.

Vitamin D helps the body absorb calcium, which is used to build and maintain bones. Low vitamin D levels have been linked to an increased risk of high blood pressure, heart attack, heart failure, stroke and diabetes. In pregnant people, low vitamin D is associated with pre-eclampsia and gestational diabetes.

Omega-3 fatty acids are used in cell membranes and help with making various hormones that regulate blood clotting and how the walls of your arteries contract and expand. They may also decrease inflammation. The Harvard T.H. Chan School of Public Health explains that your body cannot make or store omega-3 fatty acids, which necessitates regular dietary intake.

Cod Liver Oil Benefits

One teaspoon of cod liver oil provides 41 calories, 1,350 micrograms of vitamin A retinol activity equivalents (RAE) and 450 international units of vitamin D. It also provides 4.5 grams of fat, of which over 1 gram is polyunsaturated and over 2 grams are monounsaturated. Many people prefer to take cod liver oil capsules rather than taking it by the spoonful, due to the oily, fishy taste.

Many of the purported benefits of cod liver oil are due to the presence of omega-3 fatty acids. However, the National Institutes of Health Office of Dietary Supplements says the link between omega-3 fatty acids and cardiovascular health is complicated. While increased consumption of seafood may lower cardiovascular health risks, supplemental omega-3s may not provide those same benefits.

The meta-analysis found no support that omega-3 fatty acid supplements could help people suffering from coronary heart disease. Instead, the American Heart Association recommends consuming omega-3s from fish and other seafood.

Cod Liver Oil Side Effects

The Mayo Clinic says that fish oil is generally safe when taken as recommended. When taking cod liver oil, side effects range from mild to severe. The common side effects typically don't require medical attention, unless they last much longer than expected or begin to bother you. These include:

Bad breath

Headaches

Nausea

A metallic taste in the mouth

An upset stomach

There are some more serious side effects. The Cleveland Clinic recommends speaking to a doctor as soon as possible if you experience any of the following after taking cod liver oil capsules:

Allergic reactions such as skin rash, hives, itching, or swelling of the lips, face or tongue

Cod Liver Oil and Medication

Another potential side effect: Cod liver oil may interact with medications you are taking to treat other health conditions. According to MedlinePlus, be cautious about potential interactions with:

Antihypertensive drugs, taken to decrease high blood pressure. Cod liver oil may also decrease your blood pressure, causing it to become too low. Common medications for high blood pressure include amlodipine, captopril, diltiazem, enalapril, hydrochlorothiazide, losartan and valsartan.

Anticoagulant medications, taken to slow down blood clotting. Because cod liver oil can also slow down blood clotting, it may increase bruising or bleeding when combined with medications like aspirin, clopidogrel, diclofenac, dipyridamole, enoxaparin, heparin, ibuprofen and more.

If you take prescription medications, it's a good idea to speak with your doctor before adding any dietary supplements like cod liver oil to your regimen. You can ask about any potential drug interactions or side effects.

Breath and Cod Liver Oil

There are a few different things you can try if you experience bad breath after taking cod liver oil pills. One option is to take the cod liver oil capsules with food, either with a meal or a healthy snack. In particular, a meal with healthy fats like avocado or nuts may help you digest the capsules more quickly, preventing fishy breath or burping.

If taking the capsules with meals makes no difference, you might try a different brand of cod liver oil or a lower dose. You can also stop taking the supplements entirely and try to get sufficient omega-3 fatty acids from dietary sources.